API Security Checklist Every Developer Should Follow

Proactive security testing and continuous monitoring are essential for maintaining strong API security. With APIs now accounting for 83% of all web traffic, the need for thorough oversight has never been greater. Last year alone, 99% of organizations reported API security issues, with the resulting gaps costing $87 billion annually worldwide. Experts predict this number could surpass $100 billion by 2026.

Let’s dive into how automated testing and real-time monitoring can help address these challenges.

Automate API Security Testing

Manual testing simply can’t keep up with today’s rapid development cycles. Automated API security testing allows teams to catch vulnerabilities early and consistently throughout the development process. This is critical when 31% of customer-facing APIs still lack basic HTTPS encryption.

Automated testing combines various techniques to create a comprehensive security approach:

• Static Application Security Testing (SAST): Identifies vulnerabilities early in the development phase, though it may generate false positives.

• Dynamic Application Security Testing (DAST): Simulates real-world attacks but may not fully cover business logic issues.

• Penetration Testing: Uses human expertise to emulate threats but requires a significant time investment.

  In practice, once you’ve implemented security measures and controls, it’s essential to evaluate your API using both penetration testing and vulnerability scanning. Penetration testing—sometimes called ethical hacking—actively simulates attacks to reveal weaknesses that real hackers could exploit. Meanwhile, vulnerability scans systematically analyze your API for known security loopholes, often referencing standards like the OWASP Top 10 API Security Risks to ensure coverage of prevalent threats.
  
  Platforms like Qodex simplify this process by automatically scanning repositories, discovering APIs, and generating a range of tests, including unit, functional, regression, and OWASP Top 10 security tests.
  A critical component here is regression testing, which confirms that any new changes to the source code—whether you’re rolling out security patches or implementing new features—do not negatively impact or create vulnerabilities within existing functionalities. This ensures that your latest updates don’t inadvertently break what was already working or open the door to new risks.
  This automated approach covers both penetration testing—which simulates real-world attacks to uncover vulnerabilities that could be exploited by hackers—and vulnerability scanning, which checks your APIs against industry-standard risks such as those outlined in the OWASP Top 10 API Security list.

  The key is adopting a shift-left approach, integrating security testing at the earliest stages of development. Tools like StackHawk and Jit offer GitHub-native scans and automated regression testing for CI/CD pipelines. For runtime protection, platforms such as Prophaze and Salt Security provide AI-driven threat detection and low-latency blocking.

  By combining these methods, you get a comprehensive look at your API’s security posture, ensuring that common loopholes and deeper, harder-to-spot weaknesses are both identified and addressed.
  
  

Some of the functional tests generated can include:

• Smoke testing: Analyzes the most critical functionalities to quickly determine if the current build is stable.

• Sanity testing: Verifies the stability of recent changes or new features, ensuring they work as intended without disrupting existing functionality.

• Regression testing: Confirms that any changes to the source code—such as security patches or new features—haven’t inadvertently affected or broken existing features.

• Integration testing: Examines how different modules or components of the API interact with each other, identifying issues that might arise when these pieces work together.

• Usability testing: Surfaces user-facing technical issues that could negatively impact the overall user experience.

By automating this comprehensive suite of tests, these platforms help teams catch issues early and maintain confidence in each release.

API Security Testing Essentials

To ensure your APIs stand up to real-world scenarios and emerging threats, a thorough testing regimen should include:

• Functional Testing: Verifies that each endpoint and feature behaves as intended, returning the correct responses for valid and invalid requests.

• Performance Testing: Assesses how your API handles load, concurrency, and stress, helping to expose potential bottlenecks or failure points under heavy use.

• Vulnerability Scanning: Employs automated tools to continuously search for known security flaws, misconfigurations, or outdated dependencies that could be exploited.

• Penetration Testing: (Reiterating its importance) Engages skilled testers to mimic sophisticated attackers, uncovering hidden or business logic vulnerabilities that automated tools might miss.

While not all of these tests directly strengthen security, each is essential for surfacing technical issues and vulnerabilities before adversaries discover them. Regularly integrating these practices into your CI/CD pipeline ensures that your API is resilient, reliable, and ready for production.

Strengthen Defenses with API Fuzz Input Testing

Another key pillar of a robust API security strategy is fuzz input testing. In essence, fuzz testing bombards APIs with a barrage of unexpected or malformed requests—think typo-ridden inputs, random characters, or data formats your system might never expect in normal operations.

Why is this valuable? Because these "left-field" cases often reveal hidden cracks in your code, surfacing vulnerabilities that standard tests may overlook. For example, fuzzing can expose weaknesses that cause your API to behave unpredictably, generate errors, or even crash entirely—a goldmine for attackers looking for exploitable entry points.

By integrating fuzz testing with tools like Fuzzapi, Wapiti, or Wfuzz, you put your API through its paces long before cybercriminals have a chance to. This proactive approach boosts stability, hardens design, and ensures your APIs are resilient under pressure.

API Fuzz Testing Tools
To thoroughly vet your APIs against unpredictable or malicious inputs, fuzz testing should be part of your toolkit. Several popular open-source tools can help automate this process:

• Fuzzapi – Designed specifically for API fuzzing, it uncovers hidden vulnerabilities by sending a wide variety of malformed requests.

• Wapiti – Known for its flexible approach, Wapiti performs fuzz testing alongside an array of other security checks.

• Wfuzz – Useful for both fuzzing APIs and web applications, Wfuzz allows custom payloads to probe for authentication flaws and input validation issues.

Integrating these tools alongside automated SAST, DAST, and business logic tests ensures more holistic API security coverage.

Business logic testing is another critical component. Tools like Escape and Cequence excel at detecting vulnerabilities like Broken Object Level Authorization (BOLA) and Insecure Direct Object References (IDOR), offering custom test scripting for deeper analysis.

Once automated testing is in place, continuous monitoring ensures ongoing protection.

Understanding Functional Testing in API Security

Functional testing plays a pivotal role in safeguarding APIs by ensuring that all endpoints behave as intended, both individually and as a cohesive system. In this context, its main focus is to verify that security controls, features, and workflows operate precisely as designed—closing the door to vulnerabilities caused by faulty logic or overlooked requirements.

Key aspects of functional testing for API security include:

• Smoke Tests: Quickly validate that core API functions are operational, ruling out major issues before deeper testing.

• Sanity Checks: Confirm that new features or security fixes don’t introduce unexpected behavior.

• Regression Testing: Ensure recent changes—like updated authentication routines or patched vulnerabilities—haven’t impacted established functionalities or introduced new security holes.

• Integration Testing: Assess how different parts of the API interact, uncovering issues that might arise when modules connect.

• Usability and Error-Handling: Evaluate the API’s responses to invalid or malicious input, identifying gaps that could be exploited by attackers.

By embedding these functional tests into your CI/CD pipeline, you gain the confidence that critical business logic and security features remain intact—even as your API evolves and scales.

Integration Testing: Evaluating How API Modules Work Together

Integration testing steps in where unit tests leave off, focusing on the interactions between different API modules rather than isolating individual components. By simulating real-world workflows, integration tests validate that multiple modules—each of which may have been developed and tested separately—can communicate and function as a cohesive system.

This approach is critical for catching issues like misaligned data formats, broken authentication flows, or incompatible endpoint logic that only reveal themselves when modules are orchestrated together. Integration testing gives development teams confidence that, when the rubber meets the road, their APIs will operate smoothly within larger application ecosystems.

Why Ongoing API Security Testing Matters

Securing your API isn’t a “set it and forget it” exercise—even after implementing robust security tools and automated scans, continuous testing is vital. APIs evolve rapidly, with new features and updates often introducing subtle changes or hidden flaws. Each adjustment, no matter how minor, can open the door to new vulnerabilities that attackers are quick to exploit.

By regularly testing your APIs, you can:

• Catch newly introduced weaknesses before they become major headaches.

• Uncover misconfigurations or logic errors that slip past automated checks.

• Maintain visibility into how your APIs respond under real-world attack scenarios.

Even if tests aren’t strictly security-focused, they frequently surface technical issues that could lead to data leaks or breaches down the line. Consistent testing serves as both an early warning system and a health check for your API ecosystem—ensuring ongoing protection as your application evolves.

Understanding Reliability Testing for APIs

Reliability testing focuses on assessing an API’s resilience in the face of unexpected failures or disruptions. Specifically, it measures how quickly and efficiently an API can restore normal operations after an incident—think of it as a digital stress test for bounce-back ability. This process evaluates not only how fast the API recovers, but also whether automated systems can handle incidents without requiring manual intervention from developers.

By regularly performing reliability testing, teams gain valuable insights into potential weak points in error handling, system self-healing capabilities, and response time during outages. This proactive approach helps maintain high availability and trust—essentials in today’s always-on, API-driven landscape.

Volume and Capacity Testing: Uncovering Your API’s Breaking Point

Volume and capacity testing dig deep to gauge how much load your API can reliably handle before performance begins to suffer. These tests bombard your API with increasing numbers of requests to chart the tipping point—where latency rises or errors spike—offering valuable insights into scalability and reliability.

By pinpointing these boundaries, you can anticipate real-world surges in traffic, fine-tune your infrastructure, and ensure smooth experiences for users even at peak times. Volume and capacity tests, often integrated with solutions like JMeter or Gatling, help you proactively address bottlenecks long before they impact customers.

Load and Stress Testing: Gauging API Performance Under Pressure

To ensure your APIs can handle the traffic spikes and heavy workloads common in real-world environments, you’ll want to run both load and stress tests as part of your security and performance toolkit.

• Load testing simulates a typical or expected volume of requests, helping you measure how your API behaves under normal operating conditions. The goal here is to pinpoint any slowdowns or bottlenecks before your users do.

• Stress testing, in contrast, deliberately overwhelms the API with more requests than it’s designed to handle. This reveals exactly when and how your system falters—whether that’s sluggish response times or outright crashes—so you can shore up those weak points beforehand.

Together, these tests provide valuable metrics on throughput, response time, error rates, and system stability. Tools like Postman, JMeter, and Locust make it easy to automate these scenarios, ensuring your API won’t fold under pressure—whether from a Black Friday shopping rush or an unexpected viral hit.

What Is Sanity Testing in API Security?

Sanity testing serves as a quick, targeted check to confirm that recent changes or new features in your API don’t break core functionality. Think of it as the quality gate that answers: “Did our latest update actually work, or did we accidentally lock the front door with the keys inside?”

This type of testing focuses on:

• Verifying that primary endpoints respond as expected after updates

• Ensuring critical operations (like authentication, data retrieval, and input validation) still function

• Catching glaring issues that would halt further testing or release

Sanity testing doesn’t aim for exhaustive coverage. Instead, it’s the first line of defense, helping teams quickly weed out obvious failures before moving on to more comprehensive, in-depth checks like regression or security testing.

Smoke Testing: Assessing API Build Stability

Smoke testing, often referred to as "build verification testing," focuses on quickly evaluating whether the most vital endpoints and functionalities of your API are working as intended after a new build or deploy. This initial checkup doesn’t dive deep—it’s designed to catch major show-stopping errors that would make further testing pointless. In the world of API security, smoke testing helps ensure your service’s essential operations are stable enough before moving on to more thorough rounds like regression or penetration testing.

The Role of Performance Testing in API Security

Performance testing is crucial for ensuring your APIs can handle whatever the digital world throws at them—be it a sudden surge in users, unexpected traffic spikes, or just the unpredictable chaos of real-world usage. While security vulnerabilities might make headlines, slow or unreliable APIs can do just as much damage to user experience and brand trust.

At its core, performance testing evaluates how your API responds under high-stress conditions:

• Load and Stress Testing: Simulates intense usage scenarios to verify your API stays resilient under pressure without grinding to a halt or crashing.

• Volume and Capacity Testing: Helps determine the upper limits of what your API infrastructure can handle while maintaining fast response times and reliability.

• Reliability and Recovery Testing: Assesses how quickly your API can recover after failures or outages, revealing whether it can bounce back automatically or if manual intervention is needed.

By rigorously testing these dimensions, you gain insights into potential bottlenecks before they impact real users. This ensures that as your business scales—or suddenly trends on social media—your APIs are robust, minimizing downtime and service disruptions.

Performance testing, then, is not just a checkbox for compliance—it's a proactive investment in long-term stability and customer satisfaction.

Why Test Every Feature?

Every feature or functionality of your API is a potential vulnerability that attackers can exploit. Once you’ve established a solid foundation with validation and sanitization, it’s crucial to ensure your API responds correctly to both expected and unexpected inputs. Even tests that aren’t explicitly focused on security—such as those targeting performance, error handling, or business logic—can reveal hidden technical issues and vulnerabilities that cybercriminals might leverage to steal sensitive data or disrupt service.

By layering these automated and targeted testing strategies, you not only catch common mistakes but also surface deeper, less obvious flaws. This holistic approach helps protect your users and your business from evolving threats, keeping your security posture strong as your API grows and changes.

Monitor API Traffic in Real-Time

Real-time monitoring transforms security from a reactive process into a proactive one, enabling you to detect and respond to threats before they cause harm. This is particularly urgent as API usage grows rapidly - 27% of organizations report over 100% growth, while another 25% see over 50% growth in API traffic within a year.

Real-time monitoring complements secure communication practices by maintaining API integrity.

"Your API security strategy needs real-time monitoring, or it simply isn't a strategy at all. Without real-time API security monitoring, you're essentially leaving your door unlocked and hoping nobody tries the handle."
– Martyn Davies

This approach allows for immediate identification of suspicious activities, quick responses to ongoing attacks, and reduced impact from breaches. By analyzing traffic patterns and adapting to emerging threats, monitoring systems provide a dynamic layer of defense.

The benefits are clear. For example, in January 2025, Rakuten SixthSense helped a global financial institution identify and resolve 50 critical vulnerabilities in its API ecosystem, ensuring both security and compliance. Similarly, a healthcare provider used the platform to monitor 300,000 daily API calls, preventing 10 critical vulnerabilities and maintaining HIPAA compliance.

To enhance monitoring, implement unified logging and analysis for all API activity. Security Information and Event Management (SIEM) solutions can aggregate logs, detect anomalies, and provide audit trails critical for compliance and forensic investigations. AI-powered monitoring systems take this further by analyzing traffic in real-time and adapting to new attack methods as they emerge.

Real-time monitoring also supports compliance with regulations like GDPR and CCPA by continuously validating security controls and tracking access patterns.

Add Rate Limiting and Abuse Prevention

Rate limiting is a powerful tool for preventing credential stuffing, account takeovers, scraping, and resource exhaustion. By controlling the number of requests per second (TPS) or the data volume users can consume, you can mitigate many forms of abuse.

For more precise control, implement granular access restrictions based on factors like user agent, IP address, referrer, host, or geographic region. This allows you to tailor defenses to specific threat patterns while accommodating legitimate users.

For example, e-commerce platforms can combat content scraping by limiting price lookup requests. A typical strategy might allow 10 requests every 2 minutes, escalating to 20 requests every 5 minutes before blocking further attempts.

• REST API Protection: Focus on limiting POST actions and GET requests to prevent backend strain.

• GraphQL APIs: Apply limits on operations, query complexity, and individual request complexity for more effective protection.

During peak shopping seasons, an e-commerce platform resolved 25 vulnerabilities and mitigated API abuse through dynamic rate limiting, ensuring smooth operations for millions of customers.

For advanced control, use separate counting expressions to define which requests contribute to rate calculations and which are acted upon. This nuanced approach helps block abusive behavior without disrupting legitimate users.